The aims of the proposed research are to define the bioelectric properties and ion transport mechanisms of both the luminal and peritubular membranes of proximal tubule cells isolated from the cat. This objective might be achieved by aspirating single cells into the tip of a small glass capillary (lined with a silicone resin). Thus the cell would physically separate two fluid compartments. The presence of a brush border on the luminal surface of the cell facilitates achieving the proper orientation in the capillary. Measurements of the spontaneous transcellular voltage and electrical resistance of this system will be made. Microelectrodes will be utilized to measure the intracellular voltage and to provide a means of separating the electrical properties of the lumen membrane from those of the peritubular surface. The proposed research includes methods which permit the measurement of water and solute movement across single cells. The transport properties of single cells will be compared to the characteristics of intact proximal tubules (perfused in vitro). This approach could substantially improve our understanding of the integration of cellular and interspace properties which characterize the "leaky" epithelia.